Intermediate Topic How to Build a Carlson Surge Bucket, Part 1

In the late 1980s, Dr. Bruce Carlson, who was the Director of the Waikiki Aquarium, built a surge device based on information he had received from David Powell at the Monterey Aquarium. This surge equipment became known as the Carlson Surge Device or CSD.

The Carlson Surge Device is a time-tested method of creating a surge of water in an aquarium. In the days before DC controlled pumps and complex reef computers, many aquarists had one of these devices mounted to a wall over the tank.

The beauty of the surge device is that a pump degrades over time due to wear or pipe fouling, and slowly drops in flow. The surge device, however, will never degrade in strength, only the period between the surges will lengthen, as the pump feeding it wears down.

The original article by Dr. Bruce Carlson, describes in general terms how to make one of these devices, and why you might want one. The normal environment for coral reefs includes plenty of surging water and chaotic flow. Think of the ocean water moving toward the beach and then receding back. The surge helps bring food to corals and also to remove their waste.

Flow in one direction--laminar flow--is not the best for corals, and it is also not what they are used to.

That original article does not, however, get right down to the nitty-gritty of building one and leaves that as an exercise for the reader. In this article, I will drill down into those finer details of how to build a small-scale one for the home aquarium.

Why do you want one?

So, if you can put a big DC, computer-controlled powerhead on your tank these days, why would you ever want one of these? They can be noisy, generate bubbles, and don't offer the control of a modern powerhead.

Well, I don't know why you want one, but I know why I built one. For years my tank had a 10-gallon Borneman surge device running on it. Every 5 minutes or so, the sound of a toilet flush went off, and a big wave of bubbles and water came out. I hooked an auto-feeder to the surge bucket itself, so the food came down through the surge and into the tank. This worked very well, as it distributed the food evenly throughout the aquarium, and none of it ended up on the surface to be pulled away by the overflow and drains. Additionally, it would often take 2-4 flushes before all the food came out, which gave all the fish plenty of time to eat, and less ended up in some crevice to rot.

Marine fish are pretty smart too, and they quickly learned that the big blast of water sometimes had food in it. This resulted in interesting behavior. When the bubbles started leaking out of the pipe end just before the surge, they would all swim out into the open tank water. Many of them would line up on that side of the tank, excitedly swimming for the food. The blast came out, and they would swim right into the full force of the water, dancing around in the bubbles, hunting for food. Most of the time, there wasn't any, but they seemed to enjoy the blast nonetheless. This meant my fish were out and about in the front of the tank almost all the time. If you wanted to show them off, you just had to wait 5-10 minutes for the next blast, and they were all front and center.

So why not a Borneman surge device?

I ran one of these for about 5-8 years. For a long time, it worked really well, however, it had issues. One issue is that the rubber used to form the seal on the flapper slowly degrades in salt water. This meant that every six months or so, I would have to go hunt down a new flapper, and spend a day or two re-tuning the device. Also, sometimes the float would get stuck, or the chain would fall into the drain, or any number of other annoyances caused me to have to go into the room and fiddle with it.

The Borneman surge is also kind of splashy. When it fills or empties, it likes to splash water up and out of the device and onto the surrounding walls. The sound is not similar to that of a toilet; it is the exact sound of a toilet. So, you get to hear that every day forever. And finally, it creates a lot of bubbles. Far more than the Carlson. I believe the lack of moving parts in the Carlson means less maintenance, less fiddling, and more happy-fish dances.

The big picture:

Before I get into the fine details of putting together this thing, for the benefit of the DIY-challenged among the readers, let me give you the big picture in simple language:

We're going to take a bucket, and there will be three (3) pipes coming out the bottom of the bucket. There will also be some plumbing inside the bucket. Water needs to come up into the bottom of the bucket from somewhere with the help of a pump. My water comes from my sump--which sits below my display tank--and I'm using a pump that's already in place moving water up from my sump into the display tank.

The bucket will fill. (And the bucket will sit above and next to the display tank.) As the water fills the bucket, some other plumbing inside the bucket will create a siphon. When the water reaches a certain point inside the bucket, the siphon will make a lot of water will rush out of the bucket through the second pipe exiting the bottom of the bucket into the display tank. This is the surge. The water rushes out with the help of gravity.

After the surge, after the water level falls rapidly in the bucket, the siphon breaks, and the bucket will start filling again. The process repeats itself. Forever.

The third pipe exiting the bottom of the bucket is an emergency drain.

So, that's all it is in a nutshell. Let's get started.

What parts will I need?

You will need the following bits and bobs. I personally made mine from random leftover fittings I've collected over the years, so you can probably tweak the list a little, or just go right off my list to duplicate my design. My collection of selected spare bits. My surge device looks the way it does because I'm using random spare parts.

You need to cut two sections of 1.5" PVC, to connect the two elbows to the tee. They will generally end up about 1.5-2 inches in length. The reason we use the short ABS elbows, is we don't have much room in our bucket, so we need to keep the assembly pretty tight. I inserted the pipe into both ends of the tee, and then test-fitted the elbows on, until I figured out where to cut. Don't be afraid to make multiple cuts and sneak up on it. You want the elbows right up against the tee.

Don't glue anything yet. Save the glue for later, we have work to do still.

Now cut two lengths of the 1.5" pipe, so that with the pipe on the bottom of the bucket, the top of the tee is about 2 inches from the top of the bucket. Again, it's not super critical to get this right, as we will be adjusting it a lot during the tuning phase. On the end of one of the pipes, cut a long, roughly 35 degree angle off the pipe, to give it the edge you see in the picture above.

At this point, I took some sandpaper and slightly rounded the edges of the cut, inside and out, so they weren't sharp. This smooths the flow of water into the pipe when the siphon breaks and greatly cuts down on the noise.

Take the 3/4" adapter, and the 1/4" John Guest fitting, apply 2 wraps of tape to the threads, and screw them together into the top of the tee.

Now ziptie the R/O tubing to the side of the pipe with the slanted cut. Position the tubing so it is about 1" above the opening into the pipe, when viewed from the side. Connect it to the John-Guest fitting at the top of the tee, and add zipties until it is secure and isn't stressing the fitting out. You can see in mine, I used one fitting to kind of hold it against the tee, so the tubing exits vertically out of the John Guest fitting and isn't pulling to the side. You could also use a 90 degree fitting here, if you happen to find one at the hardware store.

Now why did we do it like this?

The slant-cut end of the pipe is the part that draws water in to create the siphon. If we left it flat, when the water drains down to below the opening, it will gurgle like mad and make quite a ruckus. With the slant cut, and having smoothed the edges with sandpaper, now it makes a quick gurgle, and isn't anywhere near as loud.

The R/O tubing provides a different function. When the siphon breaks, your pump is pushing water back into the system (the bucket), hopefully quickly. When it does so, it quickly stops the gurgle, and resets the device. However, there isn't much air in the pipe at this point, so what will happen is the water will form a slight siphon and actually move up the pipe and over the U-bend while the bucket is only half full. This means the device fires off once, and then just trickles water out as fast as you push it in with the pump. The R/O tubing keeps drawing in air, and breaks the siphon fully after each blast, so the pipe is ready for the next one.

Also, don't use airline tubing or soft tubing here. It makes the worst sound when it's pulling the air in, far louder than anything else this device will ever make. The R/O tubing is completely silent. It also won't get crushed by the zip ties.

Let's make a hole in a bucket!

Now it's time to cut the bottom of the bucket. You want to take the assembly, and try to fit it into the bucket. It might be tight, but the flat-bottomed pipe should sit squarely on the bottom of the bucket, and the other side shouldn't be touching the sides of the bucket. At this point you might need to go back to the previous step, and adjust things slightly until it all fits in there. In my setup, the end of the slant-cut pipe just touches the bottom of the bucket, and I have about 1.5" of gap if one side is up against the wall of the bucket.

However, it's a pretty tight fit. Flip the bucket upside down, and you will want to take the nut off the bulkhead fitting, and try to place it as close to the edge as you can. In my case, there were little angle braces around the bottom rim, that prevented me from getting right on the edge.

This is where the wood chisel comes in. Slowly and carefully use it to cut away the ridges and other things like writing that will prevent a good seal. A super sharp chisel will make quick work of this, and you can just scrape the lettering right off the bottom with ease.

The chisel is perfect for scraping and doesn't dig into the plastic like a razor blade will. Once you have it all smoothed out, place the nut where you want the hole, and use a sharpie to draw a circle on the inside of the nut.

Now take a dremel, and with one of those little drywall cutting bits, very slowly cut around the hole. You want to go slightly to the outside of the hole, but don't go crazy. If the tool slips a little, that's ok. What I like to do is cut it a bit small, test the fitting, then slowly widen it out with the tool or maybe a round file.

Don't be afraid to undercut and then slowly sneak up on it. Eventually you will have a nice clean hole, and the fitting will drop in. You should then take a file, or razor blade, and clean the edges of the hole, so you don't have any shards or things sticking out. Sandpaper works well here too.

Drop in the bulkhead, rubber gasket side on the inside of the bucket, and hand tighten the nut. Then thread one of the 1.5" male to slip adapters to the bulkhead on the inside of the bucket, and test fit your siphon assembly. With a little luck, or a little fiddling, it should all fit. Once it does, thread the other 1.5" male to slip on to the bottom of the bulkhead. Remember to use thread tape (about 2 wraps, no more than that) for these, so you don't get leaks.

Now get a hold of some spare 1.5" elbows and pipe sections, and make a small L section out of them. This small L section will be the part that goes into your display tank and will be part of your testing and tuning apparatus.

It helps to have a forgiving spouse...

For this next step, we will be invading the bathroom of your house for a few hours. You could also probably do this outdoors with a 20-40 gal bucket, or various other tubs, or even a pool if you could figure out how to suspend the bucket. I used a tub because it's way easier. No honey, I'm still in the bathroom and you can't come in yet!

Take a pair of 2x4's, and lay them across the top of the tub, so you can place the bucket on top of them, with the bulkhead between the braces. It should be reasonably stable. Now grab any old pump, hopefully somewhat similar in power to what you will ultimately be using to feed this thing, and run some tubing up into the bucket, then throw the pump in the tub. Fill the tub with water, and we are ready to begin!

Ideally, you want the L pipe you made in the last step, to end up so it is at the same depth in the water of the tub, where your eventual display will be. This step is simulating how this will work in your display tank.

So, if in the display tank, you want the top of the elbow to be 3" below the waterline, try to adjust the test tube to have the elbow at the same depth (or adjust the water in the tub, whatever works here.)

Turn on the pump, and see what happens. Generally it always works the first time, and then starts to have issues on the next refill. The water will slowly fill up and will usually go quite a bit above the top of the tee. Keep an eye on it because if you made the tee too tall, it might go above the edge of the bucket. Be ready to shut off the pump. If the bucket fills right to the rim, then take your U tube off and trim about an inch or so off each pipe, and refit.

What you should see is this: When it gets just about to the magical level where it starts to operate, you should see 5-6 large bubbles come out of the end pipe (the business end that will be in the display tank, the L). These large bubbles are the air being forced out of the U in the bucket when the siphon is being formed.

After that, you should see the water level start to drop in the bucket, and then a full siphon will begin. As the siphon finishes, the slant tube will break the siphon with a sudden gurgle. It will then start to slowly refill.

Now we can begin to tune this beast. What should happen, is that it refills, and the water just goes again. It won't, don't worry, we can fix that. First, let's discuss how the tuning works:

The depth of the L below the waterline in the bathtub impacts the height of the water in the bucket before the siphon starts. The deeper the L is in the water, the higher the water has to be above the U tube before it begins.

The power of the pump can impact the ability of the slant tube to break siphon. If the pump is too strong, the tube will not fully break siphon, and the next fill will be a fail. You can adjust this by slightly shortening the slant tube, but leaving the other tube in the U alone.

The height of the R/O tubing above the opening in the slant tube impacts how much air goes into the pipe before it refills. If your bucket fills up part way, and then you see little bubbles come out the end, but it stops filling, you don't have enough air in the U tube. What happened is you still have a partial siphon. Little bubbles bad. Big bubbles good.

If you need to "reset" it, shut the pump off and let it siphon all the water back down into the tub.

Listen for air leaks in the U tube. If your fittings, which we have not glued yet, are a bit loose sometimes they will suck in air, and this will ruin the setup. If you are absolutely sure you have the U tube and water top line set right, you can fix this by gluing it up now, though ideally, I prefer to just leave it unglued if possible. I don't ever bother to glue the U tube assembly into the bulkhead. A tiny leak there doesn't matter at all.

These things are finicky. All the different heights of things impact it. It took me about 4 hours to fully tune mine. I was very frustrated, but eventually it worked, and when it works, it just works perfectly. So just stick it out.

So the first thing you want to adjust is the overall height of the U-tube. The height of this tube determines the point at which the bucket transitions from fill to empty mode. I advise very slowly trimming it down until you get a water line you are comfortable with, maybe 2 inches below the top rim. I find it helpful to mark this somehow, so you know where it should be. You don't need the second fill to be operational at this point to adjust the top line; you can just fill it once and let it drain to figure this out.

Now we need to get the refill working. Start by moving the R/O tubing to about 1/4" above the cut of the slant tube. If the second fill doesn't trigger the siphon again (the first almost always works, it's the second that counts), then reset the device fully, move the R/O line up about 1/8", and test again. You can often tell this is the case, by removing the R/O tube from the top, and quickly putting it back in. You should hear a rush of air enter. Keep resetting and moving this line up the pipe, until you find your magical set point. Once you find it, you might want to mark your magical set point on the U-tube.

At this point, you either have it working reliably, or you have thrown it through a window. You can blame the whole thing on me to your spouse, it's OK.

Assuming you are still with me here, what I like to do at this point is leave it running for an hour or so. It should keep working. If it flakes out at some point, you probably have it very close and should only make very tiny adjustments to the R/O tube.

While I had it in the tub, firing away, I also used this opportunity to fully test the patience of my spouse and test various food types in it. Because mine will be primarily used for an auto-feeder, I want to know that food will actually fire out of it and not just rot in the bucket.

I threw a variety of different foods, pellet, flake, and shredded nori in there, and just kind of dropped them in from the top like the feeder would do, all at different water heights. Pellet food for example, would usually fully empty within 1-2 surges. Flake was more like 3, and the shredded nori was probably a bit bad for this, as it tends to get stuck on the sides. It did all empty, but only after 5-6 surges. I think I will avoid that one. I also threw a frozen food cube in, and that emptied in 3 surges.

Now I just have to clean a bunch of fish food out of the bathtub, and we'll continue with our setup next time.

This is the end of Part 1. Tomorrow we will have Part 2. Stay tuned!

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Author Profile: Tim Rightnour

Tim Rightnour has been keeping reef aquariums for about 20 years. During that time he has kept about 10 different tanks and spent countless hours building DIY devices to use in his reefkeeping adventures. He currently has a 125g softy tank, an 80g FOWLR, and an 800 gallon project tank.

Tim Rightnour deserves a special thank you for having the patience of Job explaining his surge device to me in minute detail to help me understand it and to help make his article the best it could be for everyone. Tim is a pleasure to work with.